When an engine starts, a starter or other rotating power outputting means drives the crank shaft of the engine to rotate. At this time, frictions in the engine and the compression pressure in the cylinder, particularly the compression pressure in the compression stroke, act as a resistance to the rotation. If the resistance to the rotation is too large, the engine may stop rotating immediately before the top dead center in the cylinder in the compression stroke and fail to start. In particular, in hot start, the compression pressure significantly increases, so that the start failure is likely to occur.
To avoid the start failure, there is a technique of making the rotating power outputting means intermittently apply the torque in the forward direction or alternately apply the torque in the forward direction and the reverse direction when the engine stops rotating during start (see JP03-3969A, for example).
According to the conventional technique, in which the torque is intermittently applied in the forward direction or alternately applied in the forward direction and the reverse direction, the pressure in the cylinder is released when the application of the torque is interrupted, the static friction is changed to the kinetic friction to reduce the frictional force, and an inertia torque is produced, thereby facilitating starting the engine.
There is another technique of making the rotating power outputting means drive the engine in the reverse direction at the beginning of the starting of the engine and then drive the engine in the forward direction (see JP07-71350A, for example).
In this way, the pressure in the cylinder is released when the application of the torque is interrupted, the frictional force is changed from the static frictional force to the kinetic frictional force and thereby reduced, and an inertia torque is produced, thereby facilitating starting the engine.
When an ECU is powered on, there is no information concerning the stroke of the engine at a standstill. According to these conventional techniques, the engine is controlled to start without identifying the current stroke of the engine.
That is, according to these conventional techniques, when the ECU is powered on, the stroke of the engine is not identified before a motor starting control occurs.
The conventional techniques described above do not disclose any method of identifying the state of the engine at a standstill when the ECU is powered on.
Therefore, these conventional techniques cannot be applied as they are to a technique of controlling starting of a motor depending on the stroke of the engine at a standstill, for example.